Wireless communication systems such as Long Term Evolution (LTE) systems, 5th generation (5G) wireless communication systems, and the like, are subject to many design challenges. To conserve battery power, a user equipment (UE) in such a system will often enter a low energy mode of operation when it does not have data to transmit. And to conserve radio resources, the radio access network (RAN) may not dedicate radio resources to a UE in this mode either for uplink data transmission or for signalling. As a result, a mobile UE may move into the coverage of a different cell without notifying the RAN. This mode of operation is particularly prevalent for machine-type communications (MTC) which is characterised as infrequent, often unpredictable, uplink transmission of very short data packets (e.g. tens of bytes); background traffic for web-based applications on a UE (e.g. keep-alive messages, status updates) also exhibits similar characteristics.
When a UE does have new data to transmit, there is a requirement that the UE be able to conclude the data transfer with low delay. In order to do this, mechanisms must be provided to preserve the UE context needed by the RAN to process any new transmission in order to avoid the delay and signalling overheads associated with re-creating that context. A UE operating in such a mode is said to be “dormant,” or alternatively “lightly connected” or “inactive.”
Concluding the data transfer with low delay also means that the preserved UE context must be made available for use at the new serving cell in a timely manner.
Conventionally, UE context is preserved by the network using either a centralised or distributed storage model. Centralised context data storage uses a specialised network element (e.g. a data server) to store the preserved context. Updates are forwarded to the central data store from a serving base station and retrieved from the central data store by a target or new serving base station. Like all centralised solutions, there are potential issues with responsiveness, scalability, cost, and reliability of the central data store. Distributed context data storage uses the base stations as data stores. A serving base station provides a UE with a context identifier that the UE must provide to a new serving base station. The context identifier can be used by the new serving base station to determine the base station storing the context and can be used by the storing base station to locate the preserved context. Procedures may be provided to migrate the preserved context to a different base station (e.g. the new serving base station) and to update the context identifier held by the UE. With this solution, there are potential issues with responsiveness, especially in deployments with limited connectivity between base stations, with the cost required to provide reliable data storage in a base station, and with the cost required to provide the transport facilities necessary for timely communications amongst base stations.
Therefore there is a need for a method and apparatus for storing context information that obviates or mitigates one or more limitations of the prior art.
This background information is provided to reveal information believed by the applicant to be of possible relevance to the present invention. No admission is necessarily intended, nor should be construed, that any of the preceding information constitutes prior art against the present invention.